Momordica balsamina improves glucose handling in a diet-induced prediabetic rat model

Prolonged exposure to high energy diets has been implicated in the development of pre-diabetes, a long-lasting condition that precedes type 2 diabetes mellitus (T2DM). A combination of pharmacological treatment and dietary interventions are recommended to prevent the progression of pre-diabetes to T2DM. However, poor patient compliance leads to negligence of the dietary intervention and thus reduced drug efficiency. Momordica balsamina (MB) has been reported to possess anti-diabetic effects in type 1 diabetic rats. However, the effects of this medicinal plant in conjunction with dietary intervention on pre-diabetes have not yet been established. Consequently, this study sought to evaluate the effects of MB on glucose homeostasis in a diet-induced pre-diabetes rat model in the presence and absence of dietary intervention. Pre-diabetes was induced on male Sprague Dawley rats by a high fat high carbohydrate (HFHC) diet for a period of 20 weeks. Pre-diabetic male Sprague Dawley rats were treated with MB (250 mg/kg p.o.) in both the presence and absence of dietary intervention once a day every third day for a period of 12 weeks. The administration of MB with and without dietary intervention resulted in significantly improved glucose homeostasis through reduced caloric intake, body weights, with reduced plasma ghrelin concentration and glycated hemoglobin by comparison to the pre-diabetic control. MB administration also improved insulin sensitivity as evidenced by the expression of glucose transporter 4 (GLUT 4) and glycogen synthase on the prediabetic treated animals. These results suggest that MB has the potential to be used to manage pre-diabetes and prevent the progression to overt type 2 diabetes as it demonstrated the ability to restore glucose homeostasis even in the absence of dietary and lifestyle intervention.

MAP30 and luffin-α: Novel ribosome-inactivating proteins induce plant systemic resistance against plant viruses

Ribosome-inactivating proteins (RIPs) are toxic N-glycosylase that act on eukaryotic and prokaryotic rRNAs, resulting in arrest protein synthesis. RIPs are widely found in higher plant species and display strong antiviral activity. Previous studies have shown that PAP and α-MMC have antiviral activity against TMV. However, the localization of RIPs in plant cells and the mechanism by which RIPs activate plant defense against several plant viruses remain unclear. In this study, we obtained four RIPs (the C-terminal deletion mutant of pokeweed antiviral proteins (PAP-c), alpha-momorcharin (α-MMC), momordica anti-HIV protein of 30 kDa (MAP30) and luffin-α). The subcellular localization results indicated that these four RIPs were located on the plant cell membrane. Heterologous expression of RIPs (PAP-c, α-MMC, MAP30, luffin-α) enhanced tobacco mosaic virus (TMV) resistance in N. benthamiana. Compared with the control treatment, these RIPs significantly reduced the TMV content (149-357 fold) and altered the movement of TMV in the leaves of N. benthamiana. At the same time, heterologous expression of RIPs (MAP30 and luffin-α) could relieve TMV-induced oxidative damage, significantly inducing the expression of plant defense genes including PR1 and PR2. Furthermore, application of these RIPs could inhibit the infection of turnip mosaic virus (TuMV) and potato virus x (PVX). Therefore, this study demonstrated that MAP30 and luffin-α could be considered as new, effective RIPs for controlling plant viruses by activating plant systemic defense.

The legumain McPAL1 from Momordica cochinchinensis is a highly stable Asx-specific splicing enzyme

Legumains, also known as asparaginyl endopeptidases (AEPs), cleave peptide bonds after Asn/Asp (Asx) residues. In plants, certain legumains also have ligase activity that catalyzes biosynthesis of Asx-containing cyclic peptides. An example is the biosynthesis of MCoTI-I/II, a squash family-derived cyclic trypsin inhibitor, which involves splicing to remove the N-terminal prodomain and then N-to-C-terminal cyclization of the mature domain. To identify plant legumains responsible for the maturation of these cyclic peptides, we have isolated and characterized a legumain involved in splicing, McPAL1, from Momordica cochinchinensis (Cucurbitaceae) seeds. Functional studies show that recombinantly expressed McPAL1 displays a pH-dependent, trimodal enzymatic profile. At pH 4 to 6, McPAL1 selectively catalyzed Asp-ligation and Asn-cleavage, but at pH 6.5 to 8, Asn-ligation predominated. With peptide substrates containing N-terminal Asn and C-terminal Asp, such as is found in precursors of MCoTI-I/II, McPAL1 mediates proteolysis at the Asn site and then ligation at the Asp site at pH 5 to 6. Also, McPAL1 is an unusually stable legumain that is tolerant of heat and high pH. Together, our results support that McPAL1 is a splicing legumain at acidic pH that can mediate biosynthesis of MCoTI-I/II. We purport that the high thermal and pH stability of McPAL1 could have applications for protein engineering.

Antistress and anti-aging activities of Caenorhabditis elegans were enhanced by Momordica saponin extract

BACKGROUND

Momordica saponin extract (MSE) was found to not only improve longevity and neuroprotection but also alleviate fat accumulation in Caenorhabditis elegans in our previous study. However, the lipid-lowering activity of MSE alone could not fully explain its ability to improve health, so the antistress effects of MSE were further studied.

METHODS

Using C. elegans as an in vivo animal, the lifespan of MSE-treated C. elegans under various stressors (H₂O₂, paraquat and heat) and normal conditions was studied. Furthermore, the antioxidant activities of MSE were discussed. To study the underlying mechanisms, the expression of stress resistance genes and the resistance of related mutants to H₂O₂ stress were tested.

RESULTS

MSE significantly improved the lifespan of C. elegans under stress and normal conditions. Meanwhile, the mobility of C. elegans was also improved. Moreover, the activities of SOD and CAT and the ratio of GSH/GSSG were elevated. Consistently, the levels of ROS and lipid oxidation (the NEFA and MDA content) were reduced. Furthermore, MSE treatment upregulated the expression of the sod-3, sod-5, clt-1, clt-2, hsp-16.1 and hsp-16.2 genes. All biomarkers indicated that the antistress and anti-aging activities of MSE were due to its strong antioxidant activities. Finally, MSE induced nuclear DAF-16::GFP localization. Studies with mutants revealed that skn-1 and hsf-1 were involved in the activity of MSE, which might upregulate the expression of downstream stress-responsive genes.

CONCLUSIONS

Therefore, in addition to its lipid-lowering property, the ability of MSE to improve healthspan was also attributed to the stress resistance effect. Together, MSE might serve as a lead nutraceutical in geriatric research.

Application of Raman spectroscopy in type 2 diabetes screening in blood using leucine and isoleucine amino-acids as biomarkers and in comparative anti-diabetic drugs efficacy studies

Diabetes is an irreversible condition characterized by elevated blood glucose levels. Currently, there are no predictive biomarkers for this disease and the existing ones such as hemoglobin A1c and fasting blood glucose are used only when diabetes symptoms are noticed. The objective of this work was first to explore the potential of leucine and isoleucine amino acids as diabetes type 2 biomarkers using their Raman spectroscopic signatures. Secondly, we wanted to explore whether Raman spectroscopy can be applied in comparative efficacy studies between commercially available anti-diabetic drug pioglitazone and the locally used anti-diabetic herbal extract Momordica spinosa (Gilg.)Chiov. Sprague Dawley (SD) rat’s blood was used and were pipetted onto Raman substrates prepared from conductive silver paste smeared glass slides. Prominent Raman bands associated with glucose (926, 1302, 1125 cm⁻¹), leucine (1106, 1248, 1302, 1395 cm⁻¹) and isolecucine (1108, 1248, 1437 and 1585 cm⁻¹) were observed. The Raman bands centered at 1125 cm⁻¹, 1395 cm⁻¹ and 1437 cm⁻¹ associated respectively to glucose, leucine and isoleucine were chosen as biomarker Raman peaks for diabetes type 2. These Raman bands displayed decreased intensities in blood from diabetic SD rats administered antidiabetic drugs pioglitazone and herbal extract Momordica spinosa (Gilg.)Chiov. The intensity decrease indicated reduced concentration levels of the respective biomarker molecules: glucose (1125 cm⁻¹), leucine (1395 cm⁻¹) and isoleucine (1437 cm⁻¹) in blood. The results displayed the power and potential of Raman spectroscopy in rapid (10 seconds) diabetes and pre-diabetes screening in blood (human or rat’s) with not only glucose acting as a biomarker but also leucine and isoleucine amino-acids where intensities of respectively assigned bands act as references. It also showed that using Raman spectroscopic signatures of the chosen biomarkers, the method can be an alternative for performing comparative efficacy studies between known and new anti-diabetic drugs. Reports on use of Raman spectroscopy in type 2 diabetes mellitus screening with Raman bands associated with leucine and isoleucine molecules acting as reference is rare in literature. The use of Raman spectroscopy in pre-diabetes screening of blood for changes in levels of leucine and isoleucine amino acids is particularly interesting as once elevated levels are noticed, necessary interventions to prevent diabetes development can be initiated.

Oxidative metabolites of lycopene and γ-carotene in gac (Momordica cochinchinensis)

Three new oxidative metabolites of lycopenes, (erythro)-lycopene-5,6-diol, (threo)-lycopene-5,6-diol, and 1,16-dehydro-2,6-cyclolycopene-5-ol B, and four new oxidative metabolites of γ-carotenes, 2',6'-cyclo-γ-carotene-1',5'-diol A, 2',6'-cyclo-γ-carotene-1',5'-diol B, (erythro)-γ-carotene-5,6-diol, and (threo)-γ-carotene-5,6-diol, were isolated as minor components from the aril of gac, Momordica cochinchinensis. These structures were determined on the basis of spectroscopic data, and some of them were compared to the structures of synthetic samples. Furthermore, the oxidative metabolic conversion pathways of lycopene and γ-carotene were discussed.

Inhibition of HIV-1 replication by balsamin, a ribosome inactivating protein of Momordica balsamina

Ribosome-inactivating proteins (RIPs) are endowed with several medicinal properties, including antiviral activity. We demonstrate here that the recently identified type I RIP from Momordica balsamina also possesses antiviral activity, as determined by viral growth curve assays and single-round infection experiments. Importantly, this activity is at play even as doses where the RIP has no cytotoxic effect. In addition, balsamin inhibits HIV-1 replication not only in T cell lines but also in human primary CD4⁺ T cells. This antiviral compound exerts its activity at a viral replicative step occurring later than reverse-transcription, most likely on viral protein translation, prior to viral budding and release. Finally, we demonstrate that balsamin antiviral activity is broad since it also impedes influenza virus replication. Altogether our results demonstrate that type I RIP can exert a potent anti-HIV-1 activity which paves the way for new therapeutic avenues for the treatment of viral infections.

Cyclic peptides arising by evolutionary parallelism via asparaginyl-endopeptidase-mediated biosynthesis

The cyclic miniprotein Momordica cochinchinensis Trypsin Inhibitor II (MCoTI-II) (34 amino acids) is a potent trypsin inhibitor (TI) and a favored scaffold for drug design. We have cloned the corresponding genes and determined that each precursor protein contains a tandem series of cyclic TIs terminating with the more commonly known, and potentially ancestral, acyclic TI. Expression of the precursor protein in Arabidopsis thaliana showed that production of the cyclic TIs, but not the terminal acyclic TI, depends on asparaginyl endopeptidase (AEP) for maturation. The nature of their repetitive sequences and the almost identical structures of emerging TIs suggest these cyclic peptides evolved by internal gene amplification associated with recruitment of AEP for processing between domain repeats. This is the third example of similar AEP-mediated processing of a class of cyclic peptides from unrelated precursor proteins in phylogenetically distant plant families. This suggests that production of cyclic peptides in angiosperms has evolved in parallel using AEP as a constraining evolutionary channel. We believe this is evolutionary evidence that, in addition to its known roles in proteolysis, AEP is especially suited to performing protein cyclization.

De novo transcriptome sequencing of Momordica cochinchinensis to identify genes involved in the carotenoid biosynthesis

The ripe fruit of Momordica cochinchinensis Spreng, known as gac, is featured by very high carotenoid content. Although this plant might be a good resource for carotenoid metabolic engineering, so far, the genes involved in the carotenoid metabolic pathways in gac were unidentified due to lack of genomic information in the public database. In order to expedite the process of gene discovery, we have undertaken Illumina deep sequencing of mRNA prepared from aril of gac fruit. From 51,446,670 high-quality reads, we obtained 81,404 assembled unigenes with average length of 388 base pairs. At the protein level, gac aril transcripts showed about 81.5% similarity with cucumber proteomes. In addition 17,104 unigenes have been assigned to specific metabolic pathways in Kyoto Encyclopedia of Genes and Genomes, and all of known enzymes involved in terpenoid backbones biosynthetic and carotenoid biosynthetic pathways were also identified in our library. To analyze the relationship between putative carotenoid biosynthesis genes and alteration of carotenoid content during fruit ripening, digital gene expression analysis was performed on three different ripening stages of aril. This study has revealed putative phytoene synthase, 15-cis-phytone desaturase, zeta-carotene desaturase, carotenoid isomerase and lycopene epsilon cyclase might be key factors for controlling carotenoid contents during aril ripening. Taken together, this study has also made availability of a large gene database. This unique information for gac gene discovery would be helpful to facilitate functional studies for improving carotenoid quantities.